Offhand, I would be tempted to say it is the activity of a not
exceedingly competent attacker trying to exploit a very old bug. The
sender is probing for the HTTP Authentication Bypass Issue from June 27
2001.
Original Advisory
http://www.cisco.com/warp/public/707/IOS-httplevel-pub.html
Malicious request: http://<device_addres>/level/16/exec/
Analyze the timing and source of log events to determine if it is an
automated issue.
Robert Guess
Assistant Professor, Information Systems Technology
Tidewater Community College
(757) 822-5022
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"J. Oquendo" <sil@politrix.org> 09/01/05 9:07 AM >>>
After doing some logfile analysis briefly yesterday, I noticed what
seems
to be some form of bot, worm, something, searching for what could seems
to
point to a Cisco exploitation of sorts. (http://tinyurl.com/df9d8)
All the hosts who've tried searching for the string are coming from
APNIC.
So I'm wondering... Has someone taken Michael Lynn's paper "Holy
Grail"
and produced a "DaVinci Code" to exploit the flaws Lynn spoke of...
Code snippet below is of "cisco_scanner.c" which searches for the same
particular /level/16/exec/-///pwd string however the code can be
modified
(obviously) and a search turns up less than one page of results on
Google.
Author's page seems to be gone like the wind... Anyhow.
# grep "/level/16/exec/-///" access_log |awk '{print $1,"\t\t"$7}'
58.236.50.75 /level/16/exec/-///pwd
221.141.168.137 /level/16/exec/-///pwd
221.138.93.31 /level/16/exec/-///pwd
218.53.244.16 /level/16/exec/-///pwd
222.232.84.34 /level/16/exec/-///pwd
222.238.128.14 /level/16/exec/-///pwd
218.50.74.189 /level/16/exec/-///pwd
218.239.26.42 /level/16/exec/-///pwd
218.232.83.18 /level/16/exec/-///pwd
211.208.254.67 /level/16/exec/-///pwd
whois.apnic.net $ABOVE_HOSTS
Code snippet...
/*
Multi-thread Cisco HTTP vulnerable scanner v0.2
by Inode
*/
#define HTTP_REQUEST "GET /level/16/exec/-///pwd HTTP/1.0\n\n"
So now I have yet another mod_security rule added 
SecFilterSelective THE_REQUEST "/level/16"
"redirect:http://www.cisco.com"